Add website analytics

A Tianji-style Websites section: a small tracking script, a public collection endpoint, and a
page per website with visitors, page views, visits, bounce rate, a chart and top lists for pages,
referrers, browsers, systems, devices, countries, languages and events. No cookies and no stored
IP address or user agent. SANDBAR_TRUST_PROXY makes the client address come from the proxy.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

cmd/sandbar/main.go

@@ -86,6 +86,8 @@ func main() {
 		MetricsToken: os.Getenv("SANDBAR_METRICS_TOKEN"),
 		MessageDays:  atoi("SANDBAR_MESSAGE_DAYS"),
 		CheckDays:    atoi("SANDBAR_CHECK_DAYS"),
+		HitDays:      atoi("SANDBAR_ANALYTICS_DAYS"),
+		TrustProxy:   os.Getenv("SANDBAR_TRUST_PROXY") == "1",
 		Version:      version,
 		AutoUpdate:   *autoUpdate,
 		UpdateServer: os.Getenv("SANDBAR_UPDATE_SERVER"),